The purpose of this study is to determine the pressure changes in the lymphatic and blood capillaries of rat intestinal villi during absorption and secretion of fluid. A vascular-perfused intestine is used. The procedure is the same as that described previously. A direct microinjection method of Landis is used for microvascular pressure measurement. The results of this study would provide basic information on lymph pressure and capillary pressure in the villi under normal conditions, under the influence of cholera toxin and of various vasomotor drugs or hormones, at varying arterial and venous pressures, in the normal state, after prolonged intestinal obstruction, and in hypovolemic shock.